Influence of cracks on the carbonation resistance of concrete structures

Carbonation-induced corrosion of steel rebar embedded in concrete is one of the major issues influencing durability of reinforced concrete structures. It has been acknowledged that structural cracks in concrete influences the carbon dioxide (CO2) diffusivity and accelerates the carbonation-induced reinforcement corrosion, however most of the previous studies on the carbonation induced corrosion have concentrated on the un-cracked / unloaded concrete. This study investigates the impact of cracks caused by loading on the depth of carbonation into concrete. Concrete prisms (100x100x500 mm) were subjected to four different crack widths (0, 0.05-0.15 mm, 0.15-0.25 mm and 0.25-0.35 mm) and the carbonation depth was determined using an accelerated environment test programme based on the CEN/TS 12390-10:2007 and XRD analysis. The impact of replacing OPC cement by pulverized fuel ash (PFA) and ground granulated blast furnace slag (GGBS) on the carbonation depth in cracked concrete was also investigated. The results show a considerable influence of crack width on the depth of carbonation and the X-ray powder diffraction analysis (XRD) confirms these results. The penetration of carbon dioxide and accumulation of carbonation compound (CaCO3) were found to be concentrated at crack locations, whereas the carbonation depths at other locations were found to be less than the carbonation depth in un-cracked concrete. The results also demonstrate a significant increase in the penetration of carbonation due to the addition of supplementary materials in the samples when compared to the reference mixes.